This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to identifying a low flying read/write head of a disc drive based on detection of an electro-static voltage discharge.
Disc drives are used for data storage in modern electronic products ranging from digital cameras to computers and network systems. Typically a disc drive includes a mechanical portion and an electronics portion in the form of a printed circuit board assembly that controls functions of the mechanical portion while providing a communication interface to a host being serviced by the disc drive.
Typically, the mechanical portion, or head-disc assembly, has a disc with a recording surface rotated at a constant speed by a spindle motor assembly and an actuator assembly positionably controlled by a closed loop servo system for use in accessing the stored data. The actuator assembly commonly supports a magnetoresistive read/write head that writes data to and reads data from the recording surface. Normally, the magnetoresistive read/write head uses an inductive element, or writer, to write data to and a magnetoresistive element, or reader, to read data from the recording surface.
The disc drive market continues to place pressure on the industry for disc drives with increased capacities, higher data rates and lower costs. A key aspect of achieving lower costs is an identification of marginal components as early as practical in the manufacturing process to preclude needless accrual of additional manufacturing costs and costly rework operations in subsequent processes. Additionally, an ability to identify, remove and replace marginal components from a disc drive prior to shipment is an aid in reduction of field failure and warranty expense.
A critical component of a disc drive is the magnetoresistive read/write head. As each read/write head passes through manufacturing processes in preparation for use in a disc drive, costs associated with those processes accrue and contribute to the overall cost of the disc drive. By measuring characteristics of the read/write head throughout the manufacturing process, defective and marginal read/write heads can be culled from the process before additional costs are needlessly applied.
Fly height of a read/write head is an important operating characteristic of the read/write head for proper operation of the disc drive. A read/write head with a fly height greater than a specified nominal fly height will typically display poor data transfer characteristics and is generally replaced. However, a read/write head with a fly height lower than the specified nominal fly height will typically display good data transfer characteristics and, unless detected, is generally not replaced. An undetected low fly head within a disc drive poses an increased risk to subsequent failure of the disc drive over the useful life of the disc drive.
As such, challenges remain and a need persists for effective techniques for determining a low flying read/write head within a disc drive throughout the disc drive manufacturing process. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.
In accordance with preferred embodiments, an apparatus for facilitating electrical detection of low flying read/write heads of a disc drive through implementation of a contact event detection routine is provided. A preferred embodiment of the apparatus includes a voltage source applying a voltage across the magnetoresistive element to induce an electrostatic charge on the surface of the read/write head, a test resistor positioned between the voltage source and the magnetoresistive element works in conjunction with the voltage source to limit the current through the magnetoresistive element, a control circuit monitoring voltage applied across the magnetoresistive element for detection of a contact event voltage signature, and a display device connected to the control circuit displaying the contact event voltage signature.
An alternate preferred embodiment of the apparatus includes a preamplifier/driver of the disc drive configured with a low fly height detection circuit communicating with the read/write head. The read/write head has a magnetoresistive element and an external surface, which includes an air bearing surface.
The low fly height detection circuit includes a differential voltage source applying a selected bias voltage across the magnetoresistive element to bring the magnetoresistive element to an operative state and a bias resistor connected between the differential power source and the magnetoresistive element operating in conjunction with the differential voltage source to maintain the selected bias voltage across the magnetoresistive element.
The low fly height detection circuit further includes a common mode voltage source electrically connected to the differential voltage source for use in incrementally inducing an electrostatic charge on the surface of the read/write head and a test resistor electrically connected between the common mode voltage source and the magnetoresistive element operating in conjunction with the common mode voltage source to maintain the electrostatic charge on the surface of the read/write head.
The low fly height detection circuit still further includes an output line attached between the test resistor and the magnetoresistive head for monitoring for an occurrence of the contact event voltage signature, the occurrence of the contact event voltage signature constitutes determination of a low flying read/write head.
The contact event detection routine is executable by either the preferred embodiment of the apparatus or the alternate preferred embodiment of the apparatus. Steps of contact event detection routine include, accelerating a disc to an operating rotational velocity, applying a voltage across a magnetoresistive element of the read/write head, the voltage applied across the magnetoresistive element is monitored for an occurrence of a contact event voltage signature.
Upon an occurrence of a contact event voltage signature, determining a level of the voltage applied across the magnetoresistive element concurrent with the occurrence of the contact event voltage signature is a following step, and comparing the voltage applied across the magnetoresistive element to a predetermined applied voltage threshold to determine presence of a low flying read/write head, after which each identified low flying read/write head is replaced and the routine ends.
Occurrence of a contact event voltage signature prior to reaching the predetermined applied voltage threshold identifies the read/write head as a low flying read/write head. Non-occurrence of a contact event voltage signature prior to reaching the predetermined applied voltage threshold identifies the read/write head is a non low flying read/write head.
These and various other features and advantages that characterize the claimed invention will be apparent upon reading the following detailed description and upon review of the associated drawings.